R-curve measurement of silicon nitride based ceramics at elevated temperatures with single edge notched beam specimens

In order to understand the fracture behavior of the structural ceramics at elevated temperatures, the R-curve behavior of silicon nitride based ceramics was measured by using single edge notched beam (SENB) specimens, at room and elevated temperatures. It is difficult to obtain stable fracture with the SENB method, but if we cut the straight notch deep enough, we can obtain the stable fracture in bending, even though the specimen is brittle and shows no rising R-curve behavior. This technique is easy to apply in high temperature testing. Three kinds of silicon nitride based ceramics were tested up to 1200 degreesC. We could measure the R-curve behavior, if the specimen did not show creep deformation. This technique is quite useful for discussing fracture behavior of ceramics at elevated temperatures.